This article doesn't mention it, but I wonder whether the fact that plaintiffs were pornography producers (http://paidcontent.org/2012/06/20/comcast-crushes-porn-owner...) was relevant to the court's decision. The decision is just a one-paragraph notice saying "for reasons stated in open court...", so it's hard to know. But I could see the Court being more worried about discovery being used for harassment in such a context.

On the other hand, given the lack of a written opinion, it's possible the Court didn't care about this "shakedown" aspect of the argument at all, and instead quashed the subpoenas for some more technical reason, like the improper-joinder argument that the article mentions.